The invention relates generally to seismic prospecting and, more particularly, to arrays of seismic vibrators used to transmit seismic signals during a seismic survey.
In wide-azimuth marine seismic surveying, impulsive seismic sources positioned at spaced-apart geodetic locations surrounding a survey area are fired sequentially at a predetermined shot interval. The interval is determined by the latest expected time of arrival of a reflected seismic signal at hydrophone receivers. Typically, six seismic sources are arranged to define the vertices of a hexagon surrounding the survey area. Because the six sources are fired sequentially, each firing cycle takes six shot intervals to complete.
Various methods have been used to speed up the data acquisition cycle in land seismic surveying. Land seismic surveying uses both impulsive sources and vibrator sources. Vibrator source methods include cascaded sweeps, slip-sweep, and simultaneous shooting. All these methods try to minimize the total time it takes the vibrators to transmit and the reflected signals to arrive at the listening geophones in each cycle by partly or completely overlapping the transmissions of separate vibrators or using one listening period for receiving the reflections of more than one vibrator signal. But all these methods leave room for further shortening of the cycle time for an array of vibrators.
Because of the great expense associated with conducting a land or marine seismic survey, any improvement in productivity, such as shortening the cycle time, is valuable. Thus, there is a need for improving the productivity of seismic surveys.